IMHO characters in a bitmap or jpeg or whatever consist of colored pixels, just like the rest of the image. In a text there is a relation of the characters with some kind of code like ASCII, you don't have that in an image.
Yes there is. The technology is called "OCR" or "Optical Character Recoginition". I think you can find some open source libs on the internet that do OCR. I personally use Atalasoft for OCR/Barcode recognition but you have to buy their software: http://www.atalasoft.com/products/dotimage/ocr/default.aspx
Aaaarrgg! And then to know I worked with such tools some 20 years ago :@ Hope they have improved, in these days they were not that optimal. I guess my brain is not improving and going in the opposite direction :(